Toshihiko Kadono

Velocity of finer fragments from impact

Abstract We describe the method and the result of a new experiment to obtain velocity distribution of fine ejecta fragments, from a few to a hundred microns in size, produced from basalt targets by impacts of nylon projectiles at a velocity of 3.7 km s −1 . The size distribution of holes perforated by the ejecta fragments on thin films and foils placed around the targets was investigated, and the size-velocity relation was determined with the aid of an empirical formula for threshold penetration (McDonnell and Sullivan, Hypervelocity Impacts in Space , Unit for Space Sciences, University of Kent, 1992). The velocity of the fastest fragments, at a given size, is from the extrapolation of the size-velocity relation for 1–100 mm fragments (Nakamura and Fujiwara, Icarus 92 , 132–146, 1991; Nakamura et al , Icarus 100 , 127–135, 1992). The laboratory results are also compared with those obtained from the study of secondary craters around large lunar craters (Vickery, Icarus 67 , 224–236, 1986, Geophys. Res. Lett . 14 , 726–729, 1987). All these data provide a smooth size-velocity relationship in the normalized fragment size range of four orders of magnitude.

A semi-analytical on-hugoniot eos of condensed matter using a linear UP-Us relation

Accurate equation of state (EOS) is essential for understanding a variety of geologic processes associated with shock compression of materials. A number of highly sophisticated EOSs have been proposed (e.g., M-ANEOS and SESAME), covering a wide range of P-T conditions. However, they are complex and require many model parameters. Also, there are many occasions when only terminal thermodynamic variables after adiabatic decompression are needed. For example, when the terminal molecular composition of an impact-induced vapor is necessary, only the initial entropy gain and chemical reaction processes under low-P-T conditions need to be calculated. Then, only an on-Hugoniot EOS and a low-P-T EOS are necessary. To meet such demands, we derive a new semianalytical on-Hugoniot EOS, which requires only the Hugoniot shock velocity parameters and specific heat, Gruneisen parameter, and its power-law exponent. Comparison with experimental data indicates that this EOS can reproduce on-Hugoniot entropy and temperature of ice and quartz very well, despite of its small number of model parameters.

Time-resolved spectroscopic observations of shockinduced silicate ionization

We conducted time-resolved spectroscopic observations of shock-heated quartz and forsterite using a high-power laser. The results revealed that ionization occur easily under shockinduced warm dense conditions. We compare the obtained temperatures on the Hugoniot with a few theories. The comparison suggests that the contribution of shock-induced ionization to the isochoric specific heat during shock compression is ~1 kb/atom for quartz and forsterite. Shock-induced ionization and subsequent electron recombination leads to a larger amount of vapor and may lead to dynamical and chemical evolution of silicate vapor clouds different from our current understandings.

Efficiency of linear and angular momentum transfer in oblique impact

Abstract Linear and angular momentum transfer efficiencies for oblique impacts into spherical mortar targets at velocity up to about 4 km s −1 were determined. Angular momentum transfer efficiency decreases gradually while linear momentum transfer efficiency increases with increasing impact velocity. This is understood by determining the impact-velocity dependence of both the total momentum carried by ejecta and its direction.

Measurement of expansion velocity of an impact‐generated vapor cloud

The expansion velocity of an impact-generated vapor cloud was determined. In the impact of a 7mm nylon sphere into a basaltic cube at velocity 3.8km/s, the front velocity of a luminous vapor(plasma) cloud expanding hemispherically was constant at about 4km/s within at least 5cm distance from the impact point. A simplified model calculation used to estimate the distribution of mass in the cloud suggests that most of the mass should lie near the front of the expanding cloud.